(a) Field of the Invention
The present invention is directed to a metallurgically bonded diamond-metal composite sintered material suitable in particular for lapping and method of making same.
(b) Description of the Prior Art
In the art of lapping spectacle or optical lenses, metallurgically bonded diamond-metal composite sintered materials have recently come into the limelight and among them copper-tin base alloy diamond-metal composite sintered materials have widely been used for that purpose. However, the copper-tin base alloy diamond-metal composite sintered materials are defective in that their lapping lives are exceedingly short and they are liable to seriously injure the surfaces to be lapped owing to diamond powder falling off during lapping operations. On the other hand, nickel, cobalt, iron, etc. or these base alloy diamond-metal composite sintered materials are defective in that due to their high melting points they can not be sintered sufficiently unless they are sintered at a temperature over 1000.degree. C., whereby the diamonds used are liable to rapid graphitization and consequently their characteristics are destroyed.
In order to eliminate the aforesaid deficiencies inherent to the nickel base diamond-metal composite sintered material, some of the present inventors have tried and succeeded in sintering at a low temperature, at which the diamonds used are free from graphitization, by making the particle size of the nickel powder relatively finer, and have proposed to provide a sintered material superior in the diamond-holding force as well as lapping performance (Japanese Patent Application No. 159153/1976).
However, this nickel base diamond-metal composite sintered material has proved inferior in the maintenance of lapping force because it shows gradual clogging phenomena and is deteriorated in lapping performance in the course of long-run operation.